Study of Pot Smokers' Brains Shows That MRIs Cause Bad Science Reporting


Massachusetts General

This week a study of cannabis consumers published by The Journal of Neuroscience provided powerful evidence that MRI scans cause shoddy science reporting. Researchers at Northwestern University and Massachusetts General Hospital used MRIs to compare the brains of 20 young adults who reported smoking pot at least once a week and 20 controls who had used marijuana no more than five times in their lives and had not consumed it at all in the previous year. The pot smokers had higher gray-matter densities in the left nucleus accumbens, and there were "significant shape differences" between subjects and controls in that area and in the right amygdala. The differences were more pronounced in subjects who reported smoking marijuana more frequently. "Because this is a cross-sectional study," the authors noted, "causation cannot be determined." In other words, it is not clear whether the brain differences were caused by marijuana. It also is not clear how long the differences last or whether they have any functional significance.

Those nuances generally were lost in press coverage of the study, which presented the MRI scans as evidence that smoking pot causes brain damage. News outlets claimed the study found that "marijuana re-shapes brains of users" (NBC News), that "even casually smoking marijuana can change your brain" (The Washington Post), that "casual pot use impacts brains of young adults" (The Oregonian), that "recreational pot use" is "harmful to young people's brains" (Time), that "casual marijuana use" is "bad for young adults" (The Times of India), and that "even 'casual' marijuana use can knacker bits of your brain" (Gizmodo UK). A Medical News Today headline quoted the researchers as saying "casual marijuana use changes the brain," although that statement does not appear in the article under the headline, in the study itself, or in press releases about the study issued by Northwestern University, Massachusetts General, and the Society for Neuroscience, which publishes The Journal of Neuroscience. Similarly, an MSN NZ headline had the study claiming that "cannabis use 'alters brain regions,'" another phrase that is absent from the study and the press releases.

Although they seem to have been misquoted in some cases, the researchers themselves are partly responsible for the misrepresentation of their findings. As John Gever points out in a coolheaded MedPage Today analysis, the study says "the left nucleus accumbens was consistently affected by cannabis use," even though the authors acknowledge elsewhere that their data cannot prove causation. One of the study's authors, Northwestern University psychiatrist Hans Breiter, goes even further in the Society for Neuroscience press release, saying, "This study raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences." Gever responds: "Um, no, it doesn't—not without before-and-after MRI scans showing brain structure changes in users that differ from nonusers and documentation of functional impairments associated with those changes."

Yet Breiter goes further still in the Northwestern press release. "People think a little recreational use shouldn't cause a problem, if someone is doing OK with work or school," he says. "Our data directly [say] this is not the case." No, they don't, as the study itself concedes. In the Massachusetts General press release, Breiter claims the study, which was supported by the National Institute on Drug Abuse, has policy implications: "Our findings—which need to be followed up with longer-terms studies—raise serious concerns about efforts to legalize recreational marijuana use, particularly for young adults."

What is the nature of the "bad consequences" and "problem[s]" that Breiter fears? "These two brain regions have been broadly implicated in processes underlying addiction," he says, "so it's a real problem that people claiming their marijuana use does not negatively impact their lives show significant changes in these structures." Harvard psychologist Jodie Gilman, the study's lead author, offers similar comments in the Northwestern press release. "It may be that we're seeing a type of drug learning in the brain," she says. "We think when people are in the process of becoming addicted, their brains form these new connections." It is not clear what the practical significance of "these new connections" might be, since Gilman et al. emphasize that their subjects "were not dependent" on marijuana.

Presumably Gilman and Breiter are not suggesting that anyone who smokes pot once a week is destined for addiction, which seems inconsistent with research on patterns of cannabis consumption. Data from the National Comorbidity Survey indicate that 9 percent of cannabis consumers experience "dependence" at some point in their lives. According to the National Survey on Drug Use and Health, about 18 million Americans have used marijuana in the last month, while about 3 million qualify as "dependent" at some point during a given year.

While the researchers were not always careful in explaining the significance of their findings, the misunderstandings reflected in the press coverage got a strong boost from the publicity departments at Northwestern and Massachusetts General, which picked headlines for their press releases that encouraged reporters to conflate correlation with causation and differences with damage:

Casual Marijuana Use Changes Brain Structures Involved in Reward, Emotion and Motivation: Mass. General, Northwestern Study First to Find Changes in Brains of Recreational Users

Casual Marijuana Use Linked to Brain Abnormalities: First Study to Show Effects of Small Time Use; More 'Joints' Equal More Damage

Those summaries are actually more misleading than a lot of the headlines in the general press, which is saying something.

Addendum: Pete Guither notes a scathing assessment of Gilman et al.'s study by U.C.-Berkeley computational biologist Lior Pachter, who calls it "quite possibly the worst paper I've read all year."  

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  1. Two states have legalized pot through majority vote, and polls seem to consistently show that a lot of people think pot should be legalized everywhere and that it’s relatively harmless. Yet we still see in the media, the government, and the medical community completely retarded hysteria and scaremongering regarding pot.

    Hmm, I wonder if the media, government, and medical community are filled with statist control freak scumfucks who cannot stand the idea of people doing something other than what they’re told to do.

    1. What the hell ever gave you that idea, Epi?

      1. Smoking pot.

    2. It’s no surprise with the media and government, but the degree to which doctors are for all the public heal bullshit does surprise me a bit for some reason.
      I think that a big part of the problem is that too many of them have come to see themselves as part of a health care system rather than as professionals providing a service to people, so they think it is their job to manage society’s ills.
      If someone wants their doctor to help them manage all of life’s risks, good for them. But do the fucking job people ask you to do, don’t take it upon yourself to manage everyone’s lives.

      1. Oh so true.Ive been watching this pushme pull crap since the sixties and that is the clearest and most succinct comment I’ve heard on this debate.amen

    3. My boss at work and I had lunch together today and that topic came up. She’s not a libertarian and she thinks that drug laws are stupid and immoral.

      The WOD is on the wrong side of history. It’s way past time we started to move beyond ape like barbarism.

      What happened to the age of enlightenment? We sure did get unenlightened at some point.

      1. The French Revolution was pretty much the end of any actual enlightenment.

      2. Oh, and I just remembered, our mainstream media is what brought it up.

        She had read the recent article about how some guy in CO shot his wife after allegedly consuming some pot brownies. She thought that it was absurd to just start blaming it on that when it’s too obvious that pot typically does not make people go on murderous rampages.

        So she said, ‘why does the media always do this’?

        And I just said, ‘Keeping the sheep in constant hysteria seems to be their purpose for existence. It creates a distraction so politicians can get their hands in out pockets and steal a few more of our civil liberties’.

        Hey, I fight the good fight every day. If I see an opening to preach the gospel, I take advantage.

      3. The age of enlightenment, slowly after the age of romanticism, gave way to the age of positivism, which is the age we live in now…also known as “the science is settled now shut the fuck up”

    4. Its the cartels telling them to stop the legalization trend or they’ll take the matter into their own hands.

      1. HUGE numbers of people have valuable and mature economic interests that would be threatened and in some cases blasted out of existence by legalized pot. Many of these people get on message boards and frantically throw stuff at the walls to see what sticks.

        So far, nothing is, and it is starting to p*** them off. Look for a growing backlash gaining steam probably in 2016.

    5. …a lot of people think pot should be legalized everywhere and that it’s relatively harmless. Yet we still see in the media, the government, and the medical community completely retarded hysteria and scaremongering regarding pot.”

      A lot of it is simple economic self-interest (combined with a sociopathic lack of empathy and sense of fairness. Several of the likely suspects:
      – Private prison corporations,
      – Prison guard unions,
      – Police narcotics departments,
      – Police addiction to that sweet sweet a$$et forfeiture money, cars, computers and anything else not nailed down,
      – Probation departments,
      – Big Pharma – you can’t patent a plant (Big Pharma opposition may disappear, however, if research is finally allowed and they see dollar signs in patentable specialized cannibinoid combinations that address specific illnesses)
      – Big Booze: everything from wineries, distilleries, and breweries all the way down to the local corner liquor store. This may slightly relent when someone invents a cannabis-infused and/or flavored alcoholic drink that does not get you wasted and feeling sick.
      – Existing fabric production industries
      – Existing paper production industries
      – yada yada yada.
      – And, last but certainly not least, are the Cartels. The proof of that: On YouTube enter “Drug Lord Thanks Obama, Bush, & Reagan For War On Drugs”

      – And finally we have the potential damage to the reputations of probably thousands of influential and powerful people if inconvenient truths are discovered.

    6. True then went a little over the edge.

  2. “Study of Pot Smokers’ Brains Shows That MRIs Cause Bad Science Reporting”

    Well, that’s just like, your opinion, man.

  3. Is there any reason to assume that the differences that they observed in the brains of pot smokers are necessarily harmful? It seems to me that they are making a big assumption there. Even if you could conclude a causal relationship with pot smoking, how do you know it doesn’t cause positive or completely neutral changes in the brain?

    1. It’s like the global warming climate change believers. They assume that any change can only be bad.

      1. And people who think that anything “natural” must be good for you and anything processed or “artificial” must be bad.

        1. Well, then, ask some of those people if pot is ok because it’s 100% natural.

          A lot of them will find really creative ways to twist logic into some form of hypocrisy.

          True believers believe what they do because that’s what they want to believe, and at that point, any thing objective or logical has flown out the window.

          1. A lot of “those people” do think that pot is OK for that reason. There are a lot of people who think that pot should be legal because it’s natural and shit, but are OK with other drug prohibition. Which drives me nuts. Pot shouldn’t be legalized because it’s not too bad for you (which is true), but because it is nobody’s business what drugs other people do.

            1. Pot shouldn’t be legalized because it’s not too bad for you (which is true), but because it is nobody’s business what drugs other people do.

              Of course. You and I understand this. But for a lot of people, that is just too simple for them to accept.

              And, what about that GMO pot? You know, they crossed Indica with Sativa to produce a hardier and more potent hybrid. Surely, that must be evil.

              1. “And, what about that GMO pot? You know, they crossed Indica with Sativa to produce a hardier and more potent hybrid. Surely, that must be evil.”

                heh,heh…that’s purty funny.

  4. Addendum: Pete Guither notes a scathing assessment of Gilman et al.’s study by U.C.-Berkeley computational biologist Lior Pachtel, who calls it “quite possibly the worst paper I’ve read all year.”

    I take it she hasn’t seen the latest release from the IPCC then.

    1. Perhaps she is sensible enough to consider the IPCC thing pure propaganda and not a legitimate academic paper.

    2. I’d also like to say that Pete Guither is the shit. Not only does he have a great (and pretty libertarian) blog on drug war issues, he does some pretty cool experimental theater stuff too.

  5. This is your MRI on drugs. Any questions?

  6. “even ‘casual’ marijuana use can knacker bits of your brain”


  7. I will say this about weed, from experience.

    There was a time in my youth that I smoked quite a bit of it, for several years.

    Interestingly enough, I gradually started liking it less instead of more, and it was no effort at all to stop using it. I haven’t touched it in 25 years, and have no desire to do so.

    How can that be if the brain only changes with even casual use towards learned addiction?

    Beer on the other hand, for me, I don’t know if I’ll ever stop drinking it. I don’t have a problem with doing so when I want to, but I just really, really like it, and typically don’t want to stop drinking it.

    And, Heineken is not bad beer, you damn elitist beer snobs.

    1. That seems to be what happens with a lot of pot smokers as they get older.

      Some people are just more prone to addiction than others. Anyone who thinks that drug addiction is a purely pharmacological thing is a moron.

      1. Anyone who thinks that drug addiction is a purely pharmacological thing is a moron

        I would have to agree with you. I think it’s partially pharmacological, partially genetic heredity, and partially environment.

    2. have you tried craft beer?


    Clearly, MJ has a physical affect on the brain. These images pig an inoperable. Tumor disappearing prove it. But why must the finding always demand a negative connotation?

  9. MRIs are jsut cool like that man.

  10. Or do pot smokers tend to smoke pot because of these regions in the brain?


    You’re welcome.

    1. “You’re welcome.”
      As soon as the headline reads “linked with”, I’m quite certain someone is playing lefty with the facts.

  12. Even if you could conclude a causal relationship with pot smoking, how do you know it doesn’t cause positive or completely neutral changes in the brain?

  13. Very scary if you look that

  14. This is yet another example of a study that not even its own researchers understand. The sample size is far too small to draw any conclusions–the researchers disclose this in the study, but as pointed out in the article, they then turned around and acted as though they established causation. If the best that a study can do is suggest that marijuana might cause some physical changes to the brain, and the researchers have no idea if the changes are meaningful, I’d argue that the study shouldn’t have been published. At the least, Northwestern’s PR department shouldn’t have trumpeted it with a press release.

    1. The sample size is far too small to draw any conclusions

      Precisely my first thought, the MSM is a fucking farce anymore.

    2. They have to attempt a link or possible causation to get funding to continue research with a larger group. I swear, no one knows anything about scientific research here…everyone is just paranoid.

  15. The “study” should not have made it past peer review. The sample size is too small, no causal link…at best it was something that should have been presented at a poster session during a NORML conference.

  16. I wonder if regularly fucking young, 20 something super models changes one’s brain structure?

  17. I’ve gotten to the point where I trust a scientist about as far as I can throw a politician.

  18. Who’s to say changes in the brain from smoking pot aren’t postive changes? They didn’t demonstrate any negative affects from smoking pot. All they demonstrated is that consuming pot, like vitamins, can cause changes to your organs.

    But the social conservatives are happy to see what they want to see in the study. They want to tell you what you’re doing isn’t good for you, regardless of what you think, and then to use government force to stop you from doing it, even though you’re not harming anyone else. In that aspect, they are like liberals, who see government redistribution rectifying the “injustice” of the free market, in spite of all the evidence to the contrary. And who want to use government force to redistribute your money to others because of it.

  19. Also it was a whopping 3 month study. Yea great science 20 people studied for 3 months.

  20. I smoked pot with my college buddies. Makes you feel good, but honestly, how can you say there’s no adverse effect if it “helps” you groove on the silliest things in the universe. Brave New World, eh? Truth is the best and healthiest high.

    There is a little-told story about a a battle during the Middle Ages in which one side wiped out the other side, taking advantage of their Christmas Eve drunk. I don’t mind when men lose the ability to wage war, but it also impairs the ability to defend yourself. Can you seriously say that your abilities are up to the task when you are sky-high?

    Remember, this is a guy who toked up as much as anybody for years. I don’t need a brain scan to know this.

    That said, I am absolutely 100% in favor of not only total de-criminalization but abolishing government.

  21. “You see shrinkage in the prefrontal cortex resulting from chronic stress, whereas the amygdala, the part of the brain that detects threat, starts working overtime and actually gets bigger. Thus, the more anxious and stressed you are, the more anxious you become.” – William Stixrud, Ph.D.

    Seems to me that the mechanism for amygdala enlargement was already known and that this study is backwards. People who are anxious and stressed are using cannabis to mediate symptoms and their amygdalas were already enlarged.

  22. Wow, the first study was bad…the study with 20 people in a group is even worse. Of course, everyone will believe it without further research because they like pot. Little do the sheep know research has been ongoing for years and does show that pot prematurely deteriorates the brain, and that all studies only show results for the majority, not every person. That’s why you need more than 20 people in a pot group to prove your point. Science, people. Geez.

  23. I am certain it’s not physically addictive. Every time I travel I have to give it up for the duration, and though I’m a regular user, I don’t feel the slightest need no matter how long I need to lay off, not the first day nor any day thereafter. I think it just modifies the brain by changing thought processes, like “not sweating the small stuff”. As far as I can tell the studies are asking the wrong questions and using their findings to confirm their biases.

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